A water-granulated blast furnace slag (hereinafter referred to as a "water-granulated slag") used as a raw material for cement has conventionally been manufactured by spraying pressurized cooling water onto a molten slag discharged from a blast furnace. Since the molten blast furnace slag is cooled and solidified through contact with the cooling water, the water-granulated slag thus obtained is vitrified. A water-granulated slag is usually applied as follows:
(a) as part of a raw material for a Portland cement clinker;
(b) to be added with a Portland cement; and
(c) as a raw material for a blast furnace cement.
However, because a water-granulated slag comes into direct contact with a cooling water in the course of manufacturing, it usually contains about 15 wt.% water. To apply it for any of the above-mentioned uses (a) to (c), therefore, it is necessary to dry the water-granulated slag in advance. This drying requires about 17 liters of heavy oil per ton of water-granulated slag, and in addition, transportation cost for the unnecessary water content is required when transporting the water-granulated slag before drying. For the uses (b) and (c) above, furthermore, it is necessary to finely pulverize the water-granulated slag previously until the specific surface area value based on the Blaine-air-permeability method (hereinafter referred to as the "Blaine fineness") reaches about 4,000 cm.sup.2 /g, thus requiring about 100 KWH electric power per ton of water-granulated slag. During the manufacture of the water-granulated slag, contact with the cooling water leads to the production of such noxious gases as hydrogen sulfide, resulting in worsening working environments, and moreover, useful soluble substances contained in the water-granulated slag such as lime, silica and alumina are lost by dissolution into the cooling water.
With these facts in view, the following treating process and treating apparatus of a molten blast furnace slag have been proposed.
(1) An apparatus for granulating a molten material such as a molten steel or a molten slag, disclosed in Japanese Patent Publication No. 30,149/77 dated Aug. 5, 1977, which comprises:
feeding a molten material such as a molten steel or a molten slag onto a rotary disk in rotation; granulating said molten material by causing said molten material to scatter under the effect of centrifugal force produced by the rotation of said disk; covering the periphery of said disk with a frustoconical casing flaring downwardly; forming a film of cooling water flowing downwardly along the inner surface of said casing; and, cooling and solidifying said granulated molten material by the contact with said film of flowing cooling water (hereinafter referred to as the "prior art (1)").
(2) A method for treating a molten slag, disclosed in Japanese Patent Publication No. 13,323/78 dated May 9, 1978, which comprises:
feeding a molten slag into a rotating rotary drum inclined by 2.degree. to 20.degree. relative to the horizontal line from an inlet on the higher side thereof, while cooling the barrel of said drum by spraying cooling water onto the outer surface of said drum; cooling and solidifying said molten slag by the contact with the inner surface of said drum, and at the same time, crushing said solidified slag by the rotation of said drum; and, discharging said crushed slag from an outlet on the lower side of said drum (hereinafter referred to as the "prior art (2)").
(3) An apparatus for granulating a molten slag, disclosed in Japanese Patent Provisional Publication No. 19,991/78 dated Feb. 23, 1978, which comprises:
feeding a molten slag onto the outer surface of a rotating rotary drum; granulating said molten slag by causing same to scatter in front of said drum under the effect of centrifugal force produced by the rotation of said drum; and, cooling and solidifying said granulated molten slag by a cooling system installed within the scattering area of said granulated molten slag (hereinafter referred to as the "prior art (3)")
(4) A method for manufacturing a material for blast furnace cement, disclosed in Japanese Patent Publication No. 17,829/63 dated Sept. 11, 1963, which comprises:
vitrifying a molten blast furnace slag by granulating, while cooling and solidifying, said molten blast furnace slag by blowing the molten blast furnace slag with a pressurized fluid such as a pressurized air and a pressurized steam, or by causing the molten blast furnace slag fed onto a rotating rotary disk to scatter under the effect of centrifugal force produced by the rotation of said disk; and, finely pulverizing said vitrified granulated blast furnace slag (hereinafter referred to as the "prior art (4)").
However, in any of the above-described prior arts (1) to (4), partial crystallization of molten blast furnace slag is inevitable, because it is impossible to obtain a high cooling rate sufficient to completely vitrify the molten blast furnace slag. In the prior arts (1) and (3), furthermore, problems similar to those in the water-granulated slag mentioned above are encountered, since water is still employed as the cooling medium.